Method of singulation using laser cutting

ABSTRACT

A wafer is singulated from the back-side surface of the wafer using laser ablation, thus protecting the front-side surface of the wafer and, more particularly, the integrated circuits and/or functional units on the front-side surface. Since, according to the invention, no saw blade is used, the width of the scribe lines does not need to be any larger than the width of the beam from the laser plus some minimal tolerance for alignment. As a result, using the invention, the width of scribe lines is on the order of twenty-four times smaller than the width of scribe lines required by the prior art methods.

FIELD OF THE INVENTION

The present invention relates generally to electronic components andelectronic component packaging. More particularly, the present inventionrelates to a method of singulating electronic components from a wafer.

BACKGROUND OF THE INVENTION

As is well known to those of skill in the art, integrated circuits,i.e., electronic components, are fabricated in an array on a wafer. Thewafer is then cut, sometimes called diced, to singulate the integratedcircuits from one another.

The surface of a wafer that includes the circuitry or other functionalcomponents is called the “front-side” or “first surface” of a wafer andthe opposite surface of the wafer, the surface that has no functionalcomponents or circuitry, is called the “back-side” or “second surface”of the wafer. In the prior art, individual integrated circuits weresingulated from wafers using either front-side or back-side cutting.

FIG. 1 is a cross-sectional view of a section of a wafer 10 being cutfrom a front-side surface 10F of wafer 10 in accordance with the priorart using front-side singulation methods. According to prior artfront-side singulation methods, integrated circuits 12 were formed inwafer 10 and were delineated by scribe lines 14, which included a firstscribe line 14A and a second scribe line 14B, on front-side surface 10Fof wafer 10. Scribe lines 14 were formed by methods well known to thoseof skill in the art. For example, scribe lines 14 were often formed byselective etching of a silicon oxide layer 18 on front-side surface 10F.

To illustrate, first scribe line 14A delineated a first integratedcircuit 12A from a second integrated circuit 12B. As shown in FIG. 1,each scribe line 14 had a width WF.

According to prior art front-side singulation methods, a back-sidesurface 10B of wafer 10 was attached to a tape 20. Wafer 10 was thensawed completely through with a saw blade 22. Saw blade 22 was alignedwith scribe lines 14 using an optical alignment system in a well-knownmanner. In this manner, integrated circuits 12 were singulated.According to prior art methods, tape 20 was used to support wafer 10during sawing and to support the singulated integrated circuits 12 aftersawing was complete.

Using prior art front-side singulation methods, width WF of scribe lines14 had to be sufficiently large to accommodate: the width of saw blade22; the inexact positioning and alignment of saw blade 22; themechanical wobbling of saw blade 22; and the uneven or rough surfacesresulting from the mechanical nature of the cutting using saw blade 22.Stated another way, width WF of scribe lines 14 had to be large enoughthat the saw cut made by saw blade 22 was always within a scribe line14. For example, saw blade 22 is within scribe line 14B in FIG. 1.

The optical alignment system of the prior art used scribe lines 14directly to align saw blade 22 and saw blade 22 was aligned to scribelines 14 to within a mechanically mandated tolerance. To accommodatethis tolerance, and the other factors discussed above that areassociated with any sawing processes, scribe lines 14 were madesignificantly wider than saw blade 22. To illustrate, the typical widthof saw blade 22 was between 0.001 inches (0.026 mm) and 0.002 inches(0.051 mm) while width WF of scribe line 14 was typically within therange of 0.003 inches (0.077 mm) to 0.008 inches (0.203 mm).

Disadvantageously, forming scribe lines 14 with relatively large widthsWF resulted in less integrated circuits 12 for any given size wafer 10than could be formed with smaller, more optimal, scribe line widths.This was because larger widths WF meant scribe lines 14 took up morewafer surface 10F area. This, in turn, meant more wasted wafer surface10F area and less surface 10F area available for integrated circuits 12.Consequently, the integrated circuit 12 yield per wafer 10 decreased. Asa result, the cost of each integrated circuit 12 from wafer 10 wasincreased. Unfortunately, in today's highly competitive markets it isvery important to minimize the cost of each integrated circuit 12 toremain competitive.

In certain instances, such as integrated circuits that includemicro-machines or other delicate functional components, it is importantto protect the front-side surface of the wafer during sawing from thepressure and shards and particulates generated during sawing. In theseinstances, prior art back-side singulation methods were used to saw thewafer from the back-side surface of the wafer. However, using prior artback-side singulation methods required even larger scribe line widthsand resulted in even lower integrated circuit yield per wafer.

FIG. 2 is a cross-sectional view of a section of a wafer 30 being cutfrom a back-side surface 30B of wafer 30 in accordance with the priorart. To protect a front-side surface 30F of wafer 30, front-side surface30F was attached to a tape 32. Tape 32 supported wafer 30 during sawing.

Saw blade 22 was aligned with scribe lines 14-1 on front-side surface30F of wafer 30 using a two-step process. First, tape 32 was alignedwith scribe lines 14-1. Then, front-side surface 30F was attached totape 32. Tape 32 had a surface area greater than the area of front-sidesurface 30F such that tape 32 had an exposed region, which extendedbeyond wafer 30. Tape 32 had alignment marks in the exposed region oftape 32. As an example, see alignment holes 30 a and 30 b of Roberts,Jr. et al., U.S. Pat. No. 5,362,681, which is herein incorporated byreference in its entirety. In the above manner, scribe lines 14-1 werealigned with the alignment marks of tape 32.

Second, saw blade 22 was aligned with the alignment marks of tape 32.Wafer 30 was then sawed with saw blade 22 from back-side surface 30B.However, since saw blade 22 was aligned indirectly to scribe lines 14-1using alignment marks of tape 32, a large tolerance, associated with thealignment of saw blade 22 to scribe lines 14-1, was required.

To accommodate this large tolerance, each of scribe lines 14-1 had arelatively large width WB. More particularly, referring now to FIGS. 1and 2 together, width WB of scribe lines 14-1 of wafer 30, that wasdesigned to be cut from back-side surface 30B, was significantly largerthan width WF of scribe lines 14 of wafer 10, which was designed to becut from front-side surface 10F. To illustrate, width WB was typicallyat least 0.012 inches (0.305 mm), and often even larger.

As with scribe line 14 discussed above, forming scribe lines 14-1 withrelatively large widths WB resulted in less integrated circuits 12 forany given size wafer 30. In the particular case of scribe lines 14-1 onwafer 30 in FIG. 2, the scribe lines 14-1 are even thicker than scribelines 14 in FIG. 1 and the number of integrated circuits 12 is even lessthan the corresponding number of integrated circuits 12 formed in thesame size wafer 10 in FIG. 1. Consequently, using prior art back-sidecutting as shown in FIG. 2 resulted in an even smaller yield ofintegrated circuits 12 from wafer 30. As a result, the cost of eachintegrated circuit 12 from wafer 30 was even greater than the cost ofeach integrated circuit 12 from wafer 10.

As discussed above, both front-side and back-side prior art methods ofsingulation wasted large amounts of wafers 10 and 30. This waste wasnecessary, using prior art methods, in order to create scribe lines 14and 14-1 with widths WF and WB large enough to accommodate: the width ofsaw blade 22; the inexact positioning and alignment of saw blade 22; themechanical wobbling of saw blade 22; and the uneven or rough surfacesresulting from the mechanical nature of cutting using saw blade 22.

As also discussed above, forming scribe lines 14 or 14-1 with relativelylarge widths WF and WB, as required in the prior art, resulted in lessintegrated circuits 12 for any given size wafer 10 or 30. As a result,the cost of each integrated circuit 12 from wafer 10 or 30 was greaterthan optimal. This was particularly true when prior art back-sidesingulation methods were used.

In addition, both the prior art front-side and back-side sigulationprocesses discussed above include cutting completely through wafer 10and 30 to singulate integrated circuits 12. Consequently, eachintegrated circuit 12 must be further processed, shipped and wrappedseparately, thus driving up the cost of each integrated circuit 12,increasing the probability of defective units by increasing handlingoperations and driving down the efficiency of the process.

What is needed is a method for singulating integrated circuits fromwafers that does not require the large width scribe lines of prior artmethods and therefore increases the yield per wafer and decreases thecost per integrated circuit.

SUMMARY OF THE INVENTION

As discussed above, using prior art methods of back-side singulation,scribe lines had to have widths large enough to accommodate: the widthof saw blade; the inexact positioning and alignment of saw blade; themechanical wobbling of saw blade; and the uneven or rough surfacesresulting from the mechanical nature of cutting a using saw blade. Asalso discussed above, forming the scribe lines with relatively largewidths resulted in less integrated circuits for any given size wafer,i.e., a loss of yield. This resulted in a substantial increase in thecost of the integrated circuits.

As discussed in more detail below, according to one embodiment of theinvention, a wafer is cut from the back-side surface of the wafer, thusprotecting the front-side surface of the wafer and, more particularly,the integrated circuits and/or functional units. However,advantageously, and in direct contrast to the prior art, back-sidesingulation according to the invention is preformed by a laser.Consequently, according to the invention, no saw blade is used and thewidth of the scribe lines does not need to be large enough toaccommodate: the width of saw blade; the inexact positioning andalignment of saw blade; the mechanical wobbling of saw blade; and theuneven or rough cutting surfaces left by saw blade. Stated another way,using the invention, the width of the scribe lines does not need to beany larger than the width of the beam from the laser plus some minimaltolerance for alignment. Consequently, using the invention, scribe linestypically have widths between 0.0005 inches (0.013 mm) and 0.001 inches(0.026 mm).

This is in stark contrast to the prior art methods of back-sidesingulation which required scribe lines with widths of at least 0.012inches (0.305 mm), and often even larger. As a result, using theinvention, the width of scribe lines is on the order of twenty-fourtimes smaller than the width of scribe lines required by the prior artmethods; a 2400% decrease. Therefore, using the invention, the wafer iscut from back-side surface and the integrated circuits of wafer areprotected during singulation while, at the same time, there is minimalwaste of wafer and the cost per integrated circuit is significantlylowered.

Equally impressive is the fact that, using the present invention, thewidth of the scribe lines is six to fourteen times smaller than thewidth of the scribe lines required using prior art front-sidesingulation methods. Consequently, the invention is well suited tofront-side singulation and represents a significant improvement overprior art front-side singulation methods as well.

In addition, unlike the prior art front-side and back-side sigulationprocesses discussed above, the method and structure of the inventiondoes not include cutting completely through the wafer to singulate theintegrated circuits. Consequently, each integrated circuit can befurther processed, shipped and wrapped in a wafer array, thus drivingdown the cost of each integrated circuit, decreasing the probability ofdefective units by decreasing handling operations and driving up theefficiency of the process.

In accordance with one embodiment of the present invention, a methodincludes providing a substrate, the substrate including a substratefirst surface and a substrate second surface, opposite the substratefirst surface, and a substrate thickness between the substrate firstsurface and the substrate second surface.

A scribe line is then formed on the substrate first surface, the scribeline including a scribe line width extending in a first direction on thesubstrate first surface and a scribe line length extending in a seconddirection, perpendicular to the first direction, on the substrate firstsurface, the scribe line delineating a first region of the substratefrom a second region of the substrate on the substrate first surface.

A laser beam is then aligned on the substrate second surface such thatthe laser beam is aligned on the substrate second surface with thescribe line on the substrate first surface. A trench is then created inthe substrate using the laser.

According to the invention, the trench includes: a trench opening at thesubstrate second surface, the trench opening including a trench openingwidth extending in the first direction along the substrate secondsurface; a trench depth extending from the trench opening to a trenchbottom located at a trench bottom position within the substrate, thetrench bottom including a trench bottom width extending in the firstdirection at the trench bottom position within the substrate; first andsecond trench sides extending from the trench opening to the trenchbottom; a trench length extending in the second direction on thesubstrate second surface and being at least partially coextensive withthe scribe line length on the substrate first surface such that thetrench is positioned below the scribe line within the substrate and thetrench delineates the first region of the substrate from the secondregion of the substrate on the substrate second surface.

The first region of the substrate is then singulated from the secondregion of the substrate along the trench.

In accordance with a second embodiment of the present invention, amethod includes providing a substrate, the substrate including asubstrate first surface and a substrate second surface, opposite thesubstrate first surface, and a substrate thickness between the substratefirst surface and the substrate second surface. A scribe line is thenformed on the substrate first surface, the scribe line including ascribe line width extending in a first direction on the substrate firstsurface and a scribe line length extending in a second direction,perpendicular to the first direction, on the substrate first surface,the scribe line further including a scribe line depth extending into thesubstrate first surface and a scribe line bottom surface, the scribeline delineating a first region of the substrate from a second region ofthe substrate on the substrate first surface.

A reflective layer is formed on the scribe line bottom surface. A laserscribe machine is then aligned on the substrate second surface such thata laser beam from the laser scribe machine is aligned on the substratesecond surface with the scribe line on the substrate first surface.

A portion of the substrate is then ablated from the substrate secondsurface using the laser beam, the laser beam ablating the portion of thesubstrate until the laser beam contacts the reflective layer on thescribe line bottom surface and the laser beam light is reflected fromthe reflective layer on the scribe line bottom surface. Power to thelaser beam is then removed when the laser beam light is reflected fromthe reflective layer on the scribe line bottom surface, thereby ceasingthe ablation of the substrate. In this way, the ablation of the portionof the substrate creates a trench in the substrate second surface.

According to the invention, the trench includes: a trench opening at thesubstrate second surface, the trench opening including a trench openingwidth extending in the first direction along the substrate secondsurface; a trench depth extending from the trench opening to a trenchbottom, the trench bottom including a portion of the reflective layer onthe scribe line bottom surface, the trench bottom including a trenchbottom width extending in the first direction at the reflective layer ofthe scribe line bottom surface; first and second trench sides extendingfrom the trench opening to the trench bottom; a trench length extendingin the second direction on the substrate second surface and being atleast partially coextensive with the scribe line length on the substratefirst surface such that the trench is positioned below the scribe linewithin the substrate and the trench delineates the first region of thesubstrate from the second region of the substrate on the substratesecond surface.

The first region of the substrate is then singulated from the secondregion of the substrate along the trench.

In accordance with a third embodiment of the present invention, a methodincludes providing a substrate, the substrate including a substratefirst surface and a substrate second surface, opposite the substratefirst surface, and a substrate thickness between the substrate firstsurface and the substrate second surface.

A scribe line is then formed on the substrate first surface, the scribeline including a scribe line width extending in a first direction on thesubstrate first surface and a scribe line length extending in a seconddirection, perpendicular to the first direction, on the substrate firstsurface, the scribe line delineating a first region of the substratefrom a second region of the substrate on the substrate first surface.

A laser beam is then aligned on the substrate second surface such thatthe laser beam is aligned on the substrate second surface with thescribe line on the substrate first surface. A trench is then created inthe substrate using the laser.

A portion of the substrate is then ablated from the substrate secondsurface by applying the laser beam to the substrate second surface,thereby creating a trench in the substrate.

According to the invention, the trench includes: a trench opening at thesubstrate second surface, the trench opening including a trench openingwidth extending in the first direction along the substrate secondsurface; a trench depth extending from the trench opening o a trenchbottom point located at a trench bottom position within the substrate;first and second trench sides extending from the trench opening to thetrench bottom point, such that the trench has a cross section which isapproximately triangular in shape; a trench length extending in thesecond direction on the substrate second surface and being at leastpartially coextensive with the scribe line length on the substrate firstsurface such that the trench is positioned below the scribe line withinthe substrate and the trench delineates the first region of thesubstrate from the second region of the substrate on the substratesecond surface.

The first region of the substrate is then singulated from the secondregion of the substrate along the trench.

In accordance with a fourth embodiment of the present invention, amethod includes providing a substrate, the substrate including asubstrate first surface and a substrate second surface, opposite thesubstrate first surface, and a substrate thickness between the substratefirst surface and the substrate second surface.

A scribe line is then formed on the substrate first surface, the scribeline including a scribe line width extending in a first direction on thesubstrate first surface and a scribe line length extending in a seconddirection, perpendicular to the first direction, on the substrate firstsurface, the scribe line delineating a first region of the substratefrom a second region of the substrate on the substrate first surface.

The substrate first surface is then optically scanned to locate thescribe line and determine a position of the scribe line. A firstlocation on the substrate second surface is then marked with a firstalignment mark by aiming a laser at the first location and firing thelaser. The first alignment mark is then used to determine a position ofthe scribe line and align a laser beam with the scribe line using thealignment mark such that the laser beam is aligned on the second surfaceof the substrate with the scribe line on the first surface of thesubstrate. A trench is then created in the substrate using the laser.

According to the invention, the trench includes: a trench opening at thesubstrate second surface, the trench opening including a trench openingwidth extending in the first direction along the substrate secondsurface; a trench depth extending from the trench opening to a trenchbottom located at a trench bottom position within the substrate, thetrench bottom including a trench bottom width extending in the firstdirection at the trench bottom position within the substrate; first andsecond trench sides extending from the trench opening to the trenchbottom; a trench length extending in the second direction on thesubstrate second surface and being at least partially coextensive withthe scribe line length on the substrate first surface such that thetrench is positioned below the scribe line within the substrate and thetrench delineates the first region of the substrate from the secondregion of the substrate on the substrate second surface.

The first region of the substrate is then singulated from the secondregion of the substrate along the trench.

In accordance with a third embodiment of the present invention, a methodincludes providing a wafer, the wafer including a wafer first surfaceand a wafer second surface, opposite the wafer first surface, and awafer thickness between the wafer first surface and the wafer secondsurface. A plurality of scribe lines is then formed on the wafer firstsurface, each of the scribe lines including a scribe line widthextending in a first direction on the wafer first surface and a scribeline length extending in a second direction, perpendicular to the firstdirection, on the wafer first surface, the plurality of scribe linesdelineating a plurality of regions on the wafer first surface.

A laser beam is then aligned on the wafer second surface such that thelaser beam is aligned on the wafer second surface with one scribe lineof the plurality of scribe lines on the wafer first surface. A trench isthen created in the wafer second surface using the laser.

According to the invention the trench includes: a trench opening at thewafer second surface, the trench opening including a trench openingwidth extending in the first direction along the wafer second surface; atrench depth extending from the trench opening to a trench bottomlocated at a trench bottom position within the wafer, the trench bottomincluding a trench bottom width extending in the first direction at thetrench bottom position within the wafer; first and second trench sidesextending from the trench opening to the trench bottom; a trench lengthextending in the second direction on the wafer second surface and beingat least partially coextensive with the scribe line length on the waferfirst surface such that the trench is positioned below the scribe linewithin the wafer.

Then the aligning of the laser beam on the wafer second surface andcreating a trench in the wafer second surface is repeated for each oneof the plurality of scribe lines on the wafer first surface such that aplurality of trenches are created delineating a plurality of regions onthe wafer second surface.

The plurality of regions are then singulated from the wafer along thetrenches.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a section of a wafer being cut froma front-side surface of the wafer in accordance with the prior art.

FIG. 2 is a cross-sectional view of a section of a wafer being cut froma back-side surface of the wafer in accordance with the prior art.

FIG. 3A shows a scribe grid on a front-side surface of a wafer includinghorizontal scribe lines and vertical scribe lines that define individualintegrated circuits.

FIG. 3B shows a cross-sectional view of a section of a wafer, as seenalong line IIIB—IIIB in FIG. 3A, being singulated from the back-sidesurface of the wafer according to the principles of the presentinvention.

FIG. 4 shows a cross-sectional view of a section of wafer after having atrench ablated from the back-side surface of the wafer according to theprinciples of one embodiment of the present invention.

FIG. 5 shows a cross-sectional view of a section of a wafer after havinga trench ablated from the back-side surface of the wafer according tothe principles of another embodiment of the present invention.

FIG. 6 shows a trench grid on a back-side surface of a wafer includinghorizontal trenches and vertical trenches that lie beneath thehorizontal scribe lines and vertical scribe lines that define individualintegrated circuits, according to the principles of the invention.

In the following description, the same or similar elements are labeledwith the same or similar reference numbers.

DETAILED DESCRIPTION

FIG. 3A shows a scribe grid 316 on a front-side or first surface 310F ofa wafer 310. More particularly, FIG. 3A is a top plan view of a wafer310, e.g., a substrate, in accordance with the present invention. Formedin wafer 310 are integrated circuits 312, generally referred to aselectronic components. Although integrated circuits 312 are set forth asthe electronic components formed in wafer 310, electronic componentssuch as micro-machine chips or image sensor chips are formed in wafer310 instead of integrated circuits 312 in other embodiments. Forsimplicity, integrated circuits 312 are discussed below and illustratedin the figures.

Integrated circuits 312 are delineated by a scribe grid 316, e.g., areference feature, on a front-side, e.g., first, surface 310F of wafer310. For example, scribe grid 316 is a silicon oxide layer 311 (FIG.3B), which has been selectively etched, on front-side surface 310F.

Scribe grid 316 (FIG. 3A) includes a plurality of vertical scribe lines314 and a plurality of horizontal scribe lines 315, which delineateadjacent integrated circuits 312. Generally, vertical scribe lines 314extend in a first direction, e.g., vertical in the view of FIG. 3A.Further, horizontal scribe lines 315 extend in a second directionperpendicular to the first direction, e.g., horizontal in the view ofFIG. 3A. In this embodiment, wafer 310 includes a flat 313, which is acut straight edge of wafer 310. Flat 313 extends in the seconddirection, e.g., horizontal in the view of FIG. 3A. Also shown in FIG.3A are individual scribe lines 314A and 314B defining integratedcircuits 312A and 312B.

FIG. 3B shows a cross-sectional view of a section of wafer 310, as seenalong line IIIB—IIIB in FIG. 3A, being cut from back-side or secondsurface 310B of wafer 310 according to the principles of the presentinvention. As shown in FIG. 3B, front-side surface 310F of wafer 310 isattached to a tape 332, such as Nitto blue tape, to protect front-sidesurface 310F of wafer 310 during sigulation.

A laser scribe machine 322 is aligned with a scribe line 314A of scribegrid 316 (see FIG. 3A) using alignment methods well known to those ofskill in the art. In one embodiment of the invention, laser scribemachine 322 includes a sensor 325 that receives light reflected from thetarget, i.e., back-side surface 310B. Laser scribe machines, such aslaser scribe machine 322, are well known to those of skill in the art.Consequently, the structure and operation of laser scribe machine 322will not be discussed in detail herein to avoid detracting from theinvention.

In one embodiment of the invention, laser beam 323 is precisely alignedto scribe line 314A using newer methods of alignment such as are setforth in U.S. patent application Ser. No. 09/558,392, entitled“PRECISION MARKING AND SINGULATION METHOD”, naming Thomas Glenn et al.as inventors, filed on Apr. 25, 2000 and assigned to the assignee of thepresent invention, which is incorporated herein by reference. In thisembodiment of the invention, alignment of laser scribe machine 322 isvery precise and little or no width is added to scribe line 314A toaccommodate alignment tolerances. Consequently, the extra large width ofthe prior art scribe lines, such as width WF of scribe lines 14 on wafer10 of FIG. 1 and width WB of scribe lines 14-1 wafer 30 of FIG. 2, isnot required.

Once laser scribe machine 322 is aligned, Wafer 310 is cut fromback-side surface 310B along scribe line 314A using laser beam 323 oflaser scribe machine 322. According to the invention, laser beam 323cuts or “ablates” a trench 350 from back-side surface 310B of wafer 310to a predetermined depth 352 within wafer 310. Typically, multipletrenches 350 are created on the back-side surface 310B of wafer 310 andthe length (not shown) of each trench 350 runs the entire usable length,or width, of the back-side surface 310B of wafer 310 at the position ofthe trench. In one embodiment of the invention, trenches 350 are formedunder scribe lines 314 and 315, on the back-side of wafer 310, andtherefore trenches 350 have lengths approximately equal to, and at leastpartially coextensive with, the lengths of scribe lines 314 and 315. Asdiscussed in more detail below, the depth 352 of trench 350 varies fromapplication to application. The value for depth 352 can be controlled byselecting the appropriate power setting and time of application forlaser beam 323 of laser scribe machine 322.

As can also be seen in FIG. 3B, in one embodiment of the invention,trench 350 is roughly triangular, having a relatively wide base, ortrench opening length, 354 and an apex point 356. As discussed below,this shape has several advantages.

As discussed above, in certain instances, it is important to cut thewafer from the back-side surface. However, using prior art methods,scribe lines 14-1 had to have widths WB large enough to accommodate: thewidth of saw blade 22; the inexact positioning and alignment of sawblade 22; the mechanical wobbling of saw blade 22; and the uneven orrough surfaces resulting from the mechanical nature of cutting using sawblade 22 (see FIG. 2). Also recall that the width WB of scribe lines14-1 had to be particularly large to accommodate the particularlyimprecise alignment of saw blade 22 using prior art methods.Disadvantageously, forming the scribe lines 14-1 with a relatively largewidth WB resulted in less integrated circuits for any given size wafer,i.e., a loss of yield. This resulted in a substantial increase in thecost of the integrated circuits.

According to one embodiment of the invention, wafer 310 (FIG. 3B) is cutfrom back-side surface 310B, thus protecting front-side surface 310F ofwafer 310 and, more particularly, integrated circuits 312, 312A and312B. However, advantageously, and in direct contrast to the prior art,back-side singulation according to the invention is preformed by laserbeam 323 of laser scribe machine 322. Consequently, according to theinvention, no saw blade is used and the width WL of scribe lines 314,314A and 314B does not need to be large enough to accommodate: the widthof saw blade 22; the inexact positioning and alignment of saw blade 22;the mechanical wobbling of saw blade 22; and the uneven or rough cuttingsurfaces left by saw blade 22. Stated another way, width WL of scribelines 314, 314A and 314B of the invention does not need to be any largerthan the width of laser beam 323 plus some minimal tolerance foralignment.

In addition, as discussed above, the tolerance for alignment can befurther reduced using the newer methods of alignment set forth in U.S.patent application Ser. No. 09/558,392, entitled “PRECISION MARKING ANDSINGULATION METHOD”, naming Thomas Glenn et al. as inventors, filed onApr. 25, 2000 and assigned to the assignee of the present invention,which is incorporated herein by reference. Consequently, using theinvention, scribe lines 314, 314A and 314B typically have widths WLbetween 0.0005 inches (0.013 mm) and 0.001 inches (0.026 mm).

This is in stark contrast to the prior art methods of back-side cuttingwhich required scribe lines 14-1 with widths WB of at least 0.012 inches(0.305 mm), and often even larger (FIG. 2). As a result, using theinvention, width WL of scribe lines 314, 314A and 314B is on the orderof twenty-four times smaller than the width WB of scribe lines 14-1 inthe prior art; a 2400% decrease. Therefore, using the invention, wafer310 is cut from back-side surface 310B and integrated circuits 312 ofwafer 310 are protected during singulation, while, at the same time,there is minimal waste of wafer 310 and the cost per integrated circuit312 is significantly lower than of the cost per integrated circuit usingprior art back-side singulation methods.

Equally impressive is the fact that, using the present invention, thewidth WL of scribe lines 314, 314A and 314B is six to fourteen timessmaller than the width WF of scribe lines 14 required using prior artfront-side singulation methods (FIG. 1). Consequently, the invention iswell suited to front-side singulation and represents a significantimprovement over prior art front-side singulation methods as well.

FIG. 4 shows a cross-sectional view of a section of wafer 410 afterhaving a trench 450 ablated from back-side of second surface 410Baccording to one embodiment of the present invention. Integratedcircuits 412 and 412A are embedded in wafer 410 on front-side or firstsurface 410F and include circuitry and/or functional elements.Integrated circuits 412 and 412A are delineated by a scribe line 414 onfront-side 410F, e.g., first surface 410F, of wafer 410. In oneembodiment of the invention, scribe line 414 is a silicon oxide layer411 that has been selectively etched on front-side surface 410F.

In the embodiment of the invention shown in FIG. 4, scribe line 414,includes a metallic, or otherwise highly reflective, layer 470. Metalliclayer 470 is typically aluminum, titanium, chrome, nickel, gold or anyother highly reflective material. In one embodiment of the invention,metallic layer 470 is formed by depositing a layer of metal at thebottom of scribe line 414 after scribe line 414 is etched or otherwiseformed. In another embodiment, metallic layer 470 is formed when wafer410 is formed and scribe line 414 is etched down to the underlyingmetallic layer 470. Methods for depositing and/or forming a metalliclayer, such as metallic layer 470, are well known to those of skill inthe art. Consequently, the methods of forming metallic layer 470 are notdiscussed in more detail herein to avoid detracting from the invention.

As shown in FIG. 4, front-side surface 410F of wafer 410 is attached toa tape 432, such as Nitto blue tape, to protect front-side surface 410Fof wafer 410 during sigulation. As discussed above with respect to FIG.3B, a laser scribe machine 322 (FIG. 3B) is aligned with scribe line 414(FIG. 4) using alignment methods well known to those of skill in the artand wafer 410 is cut from back-side surface 410B beneath scribe line 414using laser beam 323 of laser scribe machine 322 (FIG. 3B). As alsodiscussed above, according to the invention, laser beam 323 cuts or“ablates” trench 450 from back-side surface 410B of wafer 410 to apredetermined depth 452 within wafer 410 (FIG. 4).

In the embodiment of the invention shown in FIG. 4, the depth 452 oftrench 450 is approximately equal to the thickness 480 of wafersubstrate 482, which is typically in the range of twenty mils to thirtymils. However, the depth 452 of trench 450 can vary from application toapplication and, in this embodiment, is equal to the depth of metalliclayer 470.

In the embodiment of the invention shown in FIG. 4, sensor 325 on laserscribe machine 322 (FIG. 3B) is used to control laser beam 323 and depth452 of trench 450 (FIG. 4). In this embodiment, sensor 325 (FIG. 3B)measures the light reflected from the laser target, i.e., back-sidesurface 410B (FIG. 4). When laser beam 323 hits metallic layer 470, theamount of light reflected into sensor 325 increases significantly. Thisincreased level of reflected light is then used to shut off laser beam323 by either signaling an operator or by triggering a circuit (notshown) on laser scribe machine 322 (FIG. 3B) to cut off power to laserbeam 323. Consequently, in the embodiment of the invention shown in FIG.4, laser beam 323 is applied to back-side surface 410B, and ablatestrench 450 in back-side surface 410B, until the metallic layer 470 isreached. In this way, the depth 452 of trench 450 is preciselycontrolled by controlling the depth of metallic layer 470.

As can also be seen in FIG. 4, in one embodiment of the invention,trench 450 is generally triangular, having a relatively wide baseopening 454 with a trench opening width 454L and a narrower trenchbottom 456 with a trench bottom length 456L, approximately equal towidth WL of scribe line 414. As shown in FIG. 4, the resulting trench450 has a side 460 that is at an angle 459 to an imaginary line 458running down the center of trench 450. In one embodiment of theinvention, angle 459 is in the range of one to five degrees.

The triangular shape of trench 450 has several advantages. First, theshape allows for a minimal width WL of scribe line 414 since trench 470comes to narrow trench bottom 456 right at scribe line 414. Second, thetriangular shape is well suited to breaking, or snapping apart,individual integrated circuits 412 and 412A. In addition, less wafer 410material needs to be ablated and this, in turn, means less waste andless power used.

Unlike the prior art front-side and back-side sigulation processesdiscussed above, the method and structure of the invention does notinclude cutting completely through wafer 410 to singulate integratedcircuits 412 and 412A. Consequently, each integrated circuit 412 can befurther processed, shipped and wrapped in a wafer array, thus drivingdown the cost of each integrated circuit 412, decreasing the probabilityof defective units by decreasing handling operations and driving up theefficiency of the process.

As discussed above, in certain instances, it is important to cut thewafer from the back-side surface. Recall that, using prior art methods,scribe lines 14-1 had to have widths WB large enough to accommodate: thewidth of saw blade 22; the inexact positioning and alignment of sawblade 22; the mechanical wobbling of saw blade 22; and the uneven orrough surfaces resulting from the mechanical nature of cutting using sawblade 22 (see FIG. 2). Also recall that the width WB of scribe lines14-1 had to be particularly large to accommodate the particularlyimprecise alignment of saw blade 22 using prior art back-sidesingulation methods. Disadvantageously, forming the scribe lines 14-1with a relatively large width WB resulted in less integrated circuitsfor any given size wafer, i.e., a loss of yield. This resulted in asubstantial increase in the cost of the integrated circuits.

According to one embodiment of the invention, wafer 410 (FIG. 4) is cutfrom back-slide surface 410B, thus protecting front-side surface 410F ofwafer 410 and, more particularly, integrated circuits 412 and 412A.However, advantageously, and in direct contrast to the prior art,back-side singulation according to the invention is reformed by laserbeam 323 of laser scribe machine 322 (FIG. 3B). Consequently, width WLof scribe line 414 does not need to be any larger than the width of thebeam from laser beam 323 plus some minimal tolerance for alignment.

In addition, as discussed above, the tolerance for alignment can befurther reduced using the newer methods of alignment set forth in U.S.patent application Ser. No. 09/558,392, entitled “PRECISION MARKING ANDSINGULATION METHOD”, naming Thomas Glenn et al. as inventors, filed onApr. 25, 2000 and assigned to the assignee of the present invention,which is incorporated herein by reference.

Consequently, using the invention, scribe line 414 typically has a widthWL between 0.0005 inches (0.013 mm) and 0.001 inches (0.026 mm).

This is in stark contrast to the prior art methods of back-sidesingulation which required scribe lines 14-1 with widths WB of at least0.012 inches (0.305 mm), and often even larger (FIG. 2). As a result,using the invention, width WL of scribe line 414 (FIG. 4) is on theorder of twenty-four times smaller than the width WB of scribe lines14-1 in the prior art; a 2400% decrease.

FIG. 5 shows a cross-sectional view of a section of wafer 510 afterhaving a trench 550 ablated from back-side or second surface 510Baccording to one embodiment of the present invention. Integratedcircuits 512 and 512A are embedded in wafer 510 in front-side or firstsurface 510F and include circuitry and/or functional elements.Integrated circuits 512 and 512A are delineated by a scribe line 514 onfront-side surface 510F, e.g., first surface 510F, of wafer 510. In oneembodiment of the invention, scribe line 514 is a silicon oxide layer511 that has been selectively etched on front-side surface 510F.

As shown in FIG. 5, front-side surface 510F of wafer 510 is attached toa tape 532, such as Nitto blue tape, to protect front-side surface 510Fof wafer 510 during sigulation. As discussed above with respect to FIG.3B, a laser scribe machine 322 (FIG. 3B) is aligned with scribe line 514(FIG. 5) using alignment methods well known to those of skill in the artand wafer 510 is cut from back-side surface 510B beneath scribe line 514using laser beam 323 of laser scribe machine 322 (FIG. 3B). As alsodiscussed above, according to the invention, laser beam 323 cuts or“ablates” trench 550 from back-side surface 410B of wafer 410 to apredetermined depth 552 within wafer 510 (FIG. 5).

In the embodiment of the invention shown in FIG. 5, the depth 552 oftrench 550 is less than the thickness 580 of wafer substrate 582.However, the depth 552 of trench 550 can vary from application toapplication. In the embodiment of the invention shown in FIG. 5, thetime of application and the power level of laser beam 323 on laserscribe machine 322 (FIG. 3B) is set to control laser beam 323 and depth552 of trench 550 (FIG. 5). In this embodiment, the power level and thetime of application of laser beam 323 are pre-selected such that thedepth 552 of trench 550 is a predetermined value and trench bottom point556 of trench 550 is a predetermined distance below point 557 at thebottom of scribe line 514. In one embodiment of the invention depth 552is twenty mils to thirty mils and trench bottom point 556 lies ten tofifteen thousand angstroms below point 557 at the bottom of scribe line514. Consequently, in the embodiment of the invention shown in FIG. 5,laser beam 323 is applied to back-side surface 510B, and ablates trench550, until the depth 552 is the desired value.

As can also be seen in FIG. 5, in one embodiment of the invention,trench 550 is generally triangular, having a relatively wide baseopening 554 with trench opening length 554L and an apex or trench bottompoint 556. As shown in FIG. 5, the resulting trench 550 has a side 560that is at an angle 559 to an imaginary line 558 that runs down thecenter of trench 550. In one embodiment of the invention, angle 559 isin the range of one degree to five degrees.

The triangular shape of trench 550 has several advantages. First, asdiscussed above, trench bottom point 556 of trench 550 is apredetermined distance below point 557 at the bottom of scribe line 514.Consequently, the structural integrity of wafer 510 can be maintained,i.e., integrated circuits 512 and 512A remain attached, until pressureis applied to scribe line 514, or trench 550, and a crack 580 develops.The triangular shape of trench 550 is well suited to breaking, orsnapping apart individual integrated circuits 512 and 512A along scribeline 514 using crack 580.

The ability of wafer 510 to maintain its structural integrity meansthat, unlike the prior art front-side and back-side sigulationprocesses, integrated circuits 512 and 512A can be further processed,shipped and wrapped in a wafer array. Consequently using the structureand method of the invention, the cost of each integrated circuit 512 and512A is decreased, the probability of defective units is decreased, bydecreasing handling operations, and the efficiency of the process isincreased.

The triangular shape of trench 550 also allows for a minimal width WL ofscribe line 514 since trench 570 comes to trench bottom point 556directly below scribe line 514.

As discussed above, in certain instances, it is important to singulatethe wafer from the back-side surface. However, recall that, using priorart methods, the width WB of scribe lines 14-1 had to be particularlylarge to accommodate the particularly imprecise alignment of saw blade22. Disadvantageously, forming the scribe lines 14-1 with a relativelylarge width WB resulted in less integrated circuits for any given sizewafer, i.e., a loss of yield. This resulted in a substantial increase inthe cost of the integrated circuits.

According to one embodiment of the invention, wafer 510 (FIG. 5) is cutfrom back-side surface 510B, thus protecting front-side surface 510F ofwafer 510 and, more particularly, integrated circuits 512 and 512A.However, advantageously, and in direct contrast to the prior art,back-side singulation according to the invention is preformed by laserbeam 323 of laser scribe machine 322 (FIG. 3B). Consequently, width WLof scribe line 514 does not need to be any larger than the width oflaser beam 323 plus some minimal tolerance for alignment.

In addition, as discussed above, the tolerance for alignment can befurther reduced using the newer methods of alignment set forth in U.S.patent application Ser. No. 09/558,392, entitled “PRECISION MARKING ANDSINGULATION METHOD”, naming Thomas Glenn et al. as inventors, filed onApr. 25, 2000 and assigned to the assignee of the present invention,which is incorporated herein by reference. Consequently, using theinvention scribe line 514 typically has a width WL between 0.0005 inches(0.013 mm) and 0.001 inches (0.026 mm).

This is in stark contrast to the prior art methods of back-side cuttingwhich required scribe lines 14-1 with widths WB of at least 0.012 inches(0.305 mm), and often even larger (FIG. 2). As a result, using theinvention, width WL of scribe line 514 is on the order of twenty-fourtimes smaller than the width WB of scribe lines 14-1 in the prior art; a2400% decrease.

FIG. 6 shows a wafer 610 including trench grid 616 formed according tothe invention on a back-side surface 610B of a wafer 610 including aplurality of horizontal trenches 615 and a plurality vertical trenches614 that lie beneath horizontal scribe lines 315 and vertical scribelines 314 that define individual integrated circuits 312 on front-sidesurface 310F (FIG. 3A). Horizontal trenches 615 and vertical trenches614 are formed in accordance with the discussion above regarding FIG. 3Band FIG. 4 or FIG. 5 and run the entire usable width 652 and usablelength 650, respectively, of wafer 610 thereby delineating individualintegrated circuits 612.

As discussed above, using prior art methods of back-side singulation,scribe lines had to have widths large enough to accommodate: the widthof saw blade; the inexact positioning and alignment of saw blade; themechanical wobbling of saw blade; and the uneven or rough surfacesresulting from the mechanical nature of cutting using a saw blade. Asalso discussed above, forming the scribe lines with a relatively largewidths resulted in less integrated circuits for any given size wafer,i.e., a loss of yield. This resulted in a substantial increase in thecost of the integrated circuits.

As shown above, according to one embodiment of the invention, a wafer iscut from back-side surface, thus protecting the front-side surface ofthe wafer and, more particularly, the integrated circuits. However,advantageously, and in direct contrast to the prior art, back-sidesingulation according to the invention is preformed by a laser.Consequently, according to the invention, no saw blade is used and thewidth of the scribe lines does not need to be large enough toaccommodate: the width of saw blade; the inexact positioning andalignment of saw blade; the mechanical wobbling of saw blade; and theuneven or rough cutting surfaces left by saw blade. Stated another way,using the invention, the width of the scribe lines does not need to beany larger than the width of the beam from the laser plus some minimaltolerance for alignment.

In addition, as discussed above, the tolerance for alignment can befurther reduced using the newer methods of alignment set forth in U.S.patent application Ser. No. 09/558,392, entitled “PRECISION MARKING ANDSINGULATION METHOD”, naming Thomas Glenn et al. as inventors, filed onApr. 25, 2000 and assigned to the assignee of the present invention,which is incorporated herein by reference. Consequently, using theinvention scribe lines typically have widths between 0.0005 inches(0.013 mm) and 0.001 inches (0.026 mm).

This is in stark contrast to the prior art methods of back-side cuttingwhich required scribe lines with widths of at least 0.012 inches (0.305mm), and often even larger. As a result, using the invention, the widthof scribe lines is on the order of twenty-four times smaller than thewidth of scribe lines required by the prior art methods; a 2400%decrease. Therefore, using the invention, the wafer is cut fromback-side surface and the integrated circuits of wafer are protectedduring singulation. At the same time, there is minimal waste of waferand the cost per integrated circuit is significantly lower than of thecost per integrated circuit using prior art back-side singulationmethods.

Equally impressive is the fact that, using the present invention, thewidth of the scribe lines is six to fourteen times smaller than thewidth of the scribe lines required using prior art front-sidesingulation methods. Consequently, the invention is well suited tofront-side singulation and represents a significant improvement overprior art front-side singulation methods as well.

In addition, unlike the prior art front-side and back-side sigulationprocesses, the method and structure of the invention does not requirecutting completely through the wafer to singulate the integratedcircuits. Consequently, each integrated circuit can be furtherprocessed, shipped and wrapped in a wafer array, thus driving down thecost of each integrated circuit, decreasing the probability of defectiveunits, by decreasing handling operations, and driving up the efficiencyof the process.

This application is related to: Glenn et al., commonly assigned U.S.patent application Ser. No. 09/558,397, entitled “PRECISION ALIGNED ANDMARKED STRUCTURE”, filed Apr. 25, 2000; Glenn et al., commonly assignedU.S. patent application Ser. No. 09/558,392, entitled “PRECISION MARKINGAND SINGULATION METHOD”, filed Apr. 25, 2000; Glenn et al., commonlyassigned and co-filed U.S. patent application Ser. No. 09/xxx, xxx,entitled “STRUCTURE INCLUDING ELECTRONIC COMPONENTS SINGULATED USINGLASER CUTTING”, all of which are herein incorporated by reference intheir entirety.

The drawings and the forgoing description gave examples of the presentinvention. The scope of the present invention, however, is by no meanslimited by these specific examples. Numerous variations, whetherexplicitly given in the specification or not, such as differences instructure, dimension, and use of material, are possible.

For example, the discussion above was directed, in large part, toembodiments of the invention that used back-side singulation. However,those of skill in the art will readily recognize that, with little or nomodification, the methods of the invention discussed above can easily beapplied to front-side singuation. Back-side sigulation was thereforechosen by way of example only and the scope of the invention is at leastas broad as given by the following claims.

What is claimed is:
 1. A method comprising: providing a substrate, saidsubstrate comprising a substrate first surface and a substrate secondsurface, opposite said substrate first surface, and a substratethickness between said substrate first surface and said substrate secondsurface; forming a scribe line on said substrate first surface, saidscribe line comprising a scribe line width extending in a firstdirection on said substrate first surface and a scribe line lengthextending in a second direction, perpendicular to said first direction,on said substrate first surface, said scribe line further comprising ascribe line depth extending into said substrate first surface and ascribe line bottom surface, said scribe line delineating a first regionof said substrate from a second region of said substrate on saidsubstrate first surface; forming a reflective layer on said scribe linebottom surface; aligning a laser scribe machine on said substrate secondsurface such that a laser beam from said laser scribe machine is alignedon said substrate second surface with said scribe line on said substratefirst surface; ablating a portion of said substrate from said substratesecond surface using said laser beam, said laser beam ablating saidportion of said substrate until said laser beam contacts said reflectivelayer on said scribe line bottom surface and said laser beam light isreflected from said reflective layer on said scribe line bottom surface;removing power to said laser beam when said laser beam light isreflected from said reflective layer on said scribe line bottom surface,thereby ceasing the ablation of said substrate; wherein said ablation ofsaid portion of said substrate creates a trench in said substrate secondsurface, said trench comprising; a trench opening at said substratesecond surface, said trench opening comprising a trench opening widthextending in said first direction along said substrate second surface; atrench depth extending from said trench opening to a trench bottom, saidtrench bottom comprising a portion of said reflective layer on saidscribe line bottom surface, said trench bottom comprising a trenchbottom width extending in said first direction at said reflective layerof said scribe line bottom surface; first and second trench sidesextending from said trench opening to said trench bottom; and a trenchlength extending in said second direction on said substrate secondsurface and being at least partially coextensive with said scribe linelength on said substrate first surface such that said trench ispositioned below said scribe line within said substrate and said trenchdelineates said first region of said substrate from said second regionof said substrate on said substrate second surface; and singulating saidfirst region of said substrate from said second region of said substratealong said trench.
 2. The method of claim 1, wherein said substratethickness is in the range of approximately twenty to thirty mils andsaid trench depth is in the range of approximately ten to fifteenthousand angstroms less than twenty to thirty mils.
 3. The method ofclaim 2, wherein said trench opening width is larger than said trenchbottom width such that said trench first and second sides extend fromsaid trench opening to said trench bottom at an angle to a lineperpendicular to said second surface of said substrate.
 4. The method ofclaim 3, wherein said angle is in the range of approximately one to fivedegrees.
 5. The method of claim 1, wherein said substrate furthercomprises: functional components formed on said first surface of saidsubstrate.
 6. The method of claim 5, wherein said functional componentscomprise integrated circuits formed on said first surface of saidsubstrate.
 7. The method of claim 5, wherein said functional componentscomprise micro-machine elements.
 8. A method comprising: providing asubstrate, said substrate comprising a substrate first surface and asubstrate second surface, opposite said substrate first surface, and asubstrate thickness between said substrate first surface and saidsubstrate second surface; forming a scribe line on said substrate firstsurface, said scribe line comprising a scribe line width of between0.0005 inches (0.013 mm) and 0.002 inches (0.052 mm) extending in afirst direction on said substrate first surface and a scribe line lengthextending in a second direction, perpendicular to said first direction,on said substrate first surface, said scribe line further comprising ascribe line depth extending into said substrate first surface and ascribe line bottom surface, said scribe line delineating a first regionof said substrate from a second region of said substrate on saidsubstrate first surface; forming a reflective layer on said scribe linebottom surface; aligning a laser scribe machine on said substrate secondsurface such that a laser beam from said laser scribe machine is alignedon said substrate second surface with said scribe line on said substratefirst surface, said laser scribe machine comprising a sensor for sensingreflected laser light from said laser beam; ablating a portion of saidsubstrate from said substrate second surface using said laser beam, saidlaser beam ablating said portion of said substrate until said laser beamcontacts said reflective layer on said scribe line bottom surface andsaid laser beam light is reflected from said reflective layer on saidscribe line bottom surface; removing power to said laser beam when saidlaser beam light is reflected from said reflective layer on said scribeline bottom surface and is sensed by said sensor, thereby ceasing theablation of said substrate; wherein said ablation of said portion ofsaid substrate creates a trench in said substrate second surface, saidtrench comprising; a trench opening at said substrate second surface,said trench opening comprising a trench opening width extending in saidfirst direction along said substrate second surface; a trench depthextending from said trench opening to a trench bottom, said trenchbottom comprising a portion of said reflective layer on said scribe linebottom surface, said trench bottom comprising a trench bottom widthextending in said first direction at said reflective layer of saidscribe line bottom surface; first and second trench sides extending fromsaid trench opening to said trench bottom wherein said trench openingwidth is larger than said trench bottom width such that said trenchfirst and second sides extend from said trench opening to said trenchbottom at an angle in the range of approximately one to five degrees toa line perpendicular to said second surface of said substrate; and atrench length extending in said second direction on said substratesecond surface and being at least partially coextensive with said scribeline length on said substrate first surface such that said trench ispositioned below said scribe line within said substrate and said trenchdelineates said first region of said substrate from said second regionof said substrate on said substrate second surface; and singulating saidfirst region of said substrate from said second region of said substratealong said trench.